Handheld computing devices often allow users to input information by making direct contact with the display surfaces of the devices. For instance, a touch input mechanism provides touch input events when a user touches a display surface of the computing device with a finger (or multiple fingers). A pen input mechanism provides pen input events when a user touches the display surface with a pen device, also known as a stylus.
However, these types of interface mechanisms introduce a number of challenges. For instance, consider the case in which the computing device allows a user to input information using both a touch input mechanism and a pen input mechanism. In the course of applying a mark on the display surface with a pen device, the user may inadvertently rest his or her palm on the display surface. The computing device may then incorrectly interpret this inadvertent contact as legitimate input activity. A similar challenge may confront a user who is intentionally using the touch input mechanism. The user may attempt to apply a focused touch to a target object presented on the display surface, yet the user may accidently brush or bump his or her hand against other parts of the display surface, causing accidental input events. These problems may understandably frustrate the user if they become a frequent occurrence, or, even if uncommon, if they cause significant disruption in the task that the user is performing.